JP3358905B2 - Method for treating wastewater containing nitrate nitrogen and ammonia nitrogen - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating wastewater containing nitrate nitrogen and ammonia nitrogen. More specifically, the present invention reduces nitrate nitrogen in wastewater containing nitrate nitrogen and ammonia nitrogen at the same time to nitrite nitrogen, and then forms a nitrogen gas by a catalytic reaction with ammonia nitrogen. The present invention relates to a method for treating wastewater containing nitrate nitrogen and ammonia nitrogen, which can be easily carried out by using the method.

[0002]

2. Description of the Related Art Heretofore, as a method for treating nitrate nitrogen-containing water, a method has been known in which nitrogen is reduced with ammonia at a high temperature of 200 to 300 ° C. and under high pressure in the presence of a catalyst (Japanese Patent Application Laid-Open No. Sho 61). -222587). However, in this method, since the reaction is carried out under a high temperature and a high pressure, a device that can withstand the reaction is required, and skill in operation and security is required. On the other hand, as a method for removing ammoniacal nitrogen in wastewater, sodium nitrite, hydrogen peroxide or the like is added as an oxidizing agent in the presence of a solid catalyst supporting a noble metal or the like, and a method of removing ammoniacal nitrogen is used.
A method of converting to nitrogen by reacting at a relatively low temperature of not more than ℃ is known (JP-A-6-99180). However, this method cannot remove nitrate nitrogen. Since nitrate nitrogen and ammonia nitrogen usually coexist in the waste water discharged from the desulfurization process, such waste water is efficiently treated at a relatively low temperature, and the nitrate nitrogen and the ammonia nitrogen are simultaneously removed. There has been a need to develop a method for treating wastewater that can be removed.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a wastewater containing nitrate nitrogen and ammonia nitrogen, wherein nitrate nitrogen is reduced at a low temperature to remove coexisting nitrate nitrogen and ammonia nitrogen easily and efficiently. The purpose of the present invention is to provide a method of treating wastewater that can be performed.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to develop a method for easily removing nitrogen from wastewater containing nitrate nitrogen and ammonia nitrogen. As a result, the present inventors have converted nitrate nitrogen to hydrogen. By reducing the generated metal and then reacting the generated nitrite nitrogen and ammonia nitrogen in the presence of a catalyst, it is possible to treat wastewater containing nitrate nitrogen and ammonia nitrogen without using a high-temperature reaction. The present inventors have completed the present invention based on this finding. That is, the present invention provides: (1) In the first step, a wastewater containing nitrate nitrogen and ammonia nitrogen is brought into contact with a metal that generates hydrogen in water, and a part or all of the nitrate nitrogen in the wastewater is removed. By reducing to nitrite nitrogen and reducing the remaining nitrate nitrogen to nitrogen, the amount of nitrite nitrogen generated in the first step becomes insufficient in the reaction with ammonia nitrogen in the third step. In the second step, the treated water
After adjusting the pH to 10 or more, a coagulant is added to remove the metal eluted in the first step by a softening treatment. In the third step, the ammonia nitrogen in the waste water and the nitrite nitrogen generated in the first step are removed. When reacting with in the presence of a catalyst,
A wastewater containing nitrate nitrogen and ammonia nitrogen, wherein an oxidizing agent corresponding to the amount of nitrite nitrogen insufficient for the reaction equivalent is added to convert ammonia nitrogen and nitrite nitrogen to nitrogen. And (2) a method for treating wastewater containing nitrate nitrogen and ammonia nitrogen according to item 1, wherein the oxidizing agent added in the third step is nitrite nitrogen. Is what you do. Furthermore, as a preferred embodiment of the present invention, (3) the first and second metals in which the metal generating hydrogen in water is zinc
(4) The method for treating wastewater containing nitrate nitrogen and ammonia nitrogen according to (1), and (4) the nitrate nitrogen and ammonia according to (1) to (3), wherein the catalyst is platinum supported on titania or γ-alumina. And a method for treating wastewater containing neutral nitrogen.

[0005] In the first step of the method of the present invention, the waste water containing nitrate nitrogen and ammonia nitrogen is brought into contact with a metal that generates hydrogen in the water to convert the nitrate nitrogen to nitrite nitrogen or nitrogen gas. To reduce. The concentration of nitrate nitrogen in the wastewater to which the method of the present invention can be applied is not particularly limited, but wastewater containing nitrate nitrogen at a concentration of 0.2 to 120 mg / liter can be particularly preferably treated. . As the metal that generates hydrogen in water, for example, Devarda alloy, zinc, aluminum, copper-cadmium alloy,
A copper-iron alloy can be used. The Devarda alloy consists of 50% by weight of copper, 5% by weight of zinc and 4% of aluminum.
An alloy comprising 5% by weight is preferable because it exhibits strong reducing power. These metals generate nascent hydrogen in water and reduce nitrate nitrogen to nitrite nitrogen or nitrogen gas as shown in the following chemical formula. ^{_{NO 3 - + 2H → NO 2}} - + H 2 O 2NO 3 - + 10H → N 2 + 4H 2 O + 2OH - In the first step of the process of the present invention, no particular restriction on the method of contacting the nitrate nitrogen and metals, for example, waste water Examples of the method include a method of adding a metal to a storage tank and stirring the mixture, and a method of passing wastewater through a filling tank filled with the metal. The processing temperature in this step is from room temperature to 80 ° C, preferably from 30 to 50 ° C.
C is appropriate. As a heating method, a method of supplying heated waste water to a stirring and mixing tank or a filling tank, a method of heating the entire reaction system, or a method combining these methods can be adopted. The processing time of this step is 0.2 hours or more in the case of a batch type, preferably 0.5 to 2 hours,
When water is passed through the filling tank, SV is preferably set to 0.1 to 10 hr ^-1 , preferably 0.5 to 2 hr ^-1 . In addition, the pH during the reaction is 10 or more when using a Devarda alloy,
It is preferably 10 to 13, preferably 6 or less, preferably 2 to 4 in the case of zinc, and around neutral in the case of aluminum, copper-cadmium alloy or copper-iron alloy. The pH can be adjusted by adding sodium hydroxide, potassium hydroxide, hydrochloric acid, sulfuric acid, or the like. In the first step, the generation ratio of nitrite nitrogen and nitrogen gas varies depending on the above-mentioned conditions such as temperature, time, and pH, but it is preferable that the reaction is performed so that nitrate nitrogen does not substantially exist.

In the second step of the method of the present invention, the metal eluted in the first step is removed by a softening treatment.
That is, after the treatment water of the first step is subjected to the coagulation treatment, solid-liquid separation is performed. In the coagulation treatment, the pH of the treated water is adjusted to 10 or more, preferably 11 or more, and the mixture is stirred vigorously for 30 minutes or more, then the stirring is loosened. Then, the coagulant is added and the mixture is stirred gently for 2 to 3 minutes and then left standing. Preferably, the aggregates are settled. Adjustment of the pH, for example, sodium hydroxide,
It can be carried out by adding an alkali such as potassium hydroxide in the form of an aqueous solution or a solid. By adjusting the pH of the treated water in the first step to 10 or more, the metal eluted in the first step contained in the wastewater is precipitated as a hydroxide. In the second step, a coagulant is added to the treated water in which the metal hydroxide has been precipitated as alkaline, to coagulate the metal hydroxide and promote sedimentation. There is no particular limitation on the flocculant used, for example, polyaluminum chloride,
Inorganic flocculants such as ferric sulfate, sodium polyacrylate, anionic polymer flocculants such as polyacrylamide partial hydrolyzate, polyaminoalkyl methacrylate,
Examples include cationic polymer flocculants such as polyethyleneimine, and nonionic polymer flocculants such as polyacrylamide and polyethylene oxide. After allowing the precipitate to coagulate and settle, the supernatant liquid is removed as it is or, if necessary, by filtration to remove fine suspended substances that have not settled and separated. The filter used is not particularly limited, and for example, a filter filled with sand or anthracite, a cartridge filter, a membrane separation device, or the like can be used. The supernatant or filtrate from which the precipitate has been separated and removed is then adjusted to a pH of 4 to 9, preferably 6 to 8, in a pH adjusting tank. The acid used for pH adjustment is not particularly limited, and for example, sulfuric acid, hydrochloric acid, and the like can be used.

In the third step of the method of the present invention, the nitrite nitrogen produced by the reduction in the first step is reacted with ammonia nitrogen originally contained in the wastewater in the presence of a catalyst to convert it into nitrogen. . When the amount of the nitrite nitrogen generated in the first step is insufficient for the reaction with the ammonia nitrogen, an oxidizing agent such as sodium nitrite and hydrogen peroxide is further added to the treated water to react. When the nitrite nitrogen generated by the reduction in the first step is present in an excessive amount with respect to the ammonia nitrogen, ammonia water or an ammonium salt is added to the treated water to react in the presence of a catalyst. be able to. When the oxidizing agent is nitrite nitrogen, ammonium ions and nitrite ions react according to the following equation. _{^{NH 4 + + NO 2 - →}} N 2 + 2H 2 O Typically, for an ammonium ion 1 mole, nitrite ions 0.5 to 1.5 mol, nitrous preferably such that 0.9 to 1.1 moles Add nitrate. When the oxidizing agent is hydrogen peroxide, ammonium ions and hydrogen peroxide react according to the following equation. 2NH ₄ ⁺ + 3H ₂ O ₂ → N ₂ + 6H ₂ O + 2H ^{+ Since} ammonium ions and hydrogen peroxide react at a molar ratio of 1: 1.5, the amount of hydrogen peroxide to be added is set in the same manner as for nitrite. can do. The amount of hydrogen peroxide used is 1.0 of ammonium ions present in the treated water.
The molar ratio is preferably up to 3.0 times. If the amount of hydrogen peroxide used is less than 1.0 mole times the ammonium ion, the ammonium ion may not be completely decomposed by the hydrogen peroxide and may remain in the wastewater. Even if the amount of hydrogen peroxide used exceeds 3.0 mole times of ammonium ion, the efficiency of removing the remaining ammonium ions does not improve in proportion to the increase in the amount of added hydrogen peroxide. In the method of the present invention, it is also possible to use nitrite and hydrogen peroxide together as an oxidizing agent, first decompose ammonium ions using nitrite, and then decompose the remaining ammonium ions by adding hydrogen peroxide. is there.

The catalyst used in the third step includes platinum, palladium, ruthenium, rhodium, indium, iridium, silver, gold, cobalt, nickel and tungsten as active components of the catalyst, and water-insoluble or hardly water-soluble metals. Compounds, for example, cobalt monoxide, nickel monoxide, ruthenium dioxide, rhodium trioxide, palladium monoxide, iridium dioxide, oxides such as tungsten dioxide, and also ruthenium dichloride, chlorides such as platinum dichloride, ruthenium sulfide , One or more selected from the group consisting of sulfides such as rhodium sulfide, α-alumina, γ-alumina, activated carbon, titania, zirconia, zeolite, glass, silica, silica-alumina, ion-exchange resin, etc. Supported on a carrier . The amount of the supported metal or compound thereof in such a supported catalyst is usually 0.05 to 5 times the weight of the carrier.
It is desirably 25% by weight, preferably 0.5 to 3% by weight. Such supported catalysts are spherical, pellet-like,
It can be used in various forms such as a column, a crushed piece, a honeycomb, and a powder. Particularly, a catalyst in which platinum is supported on a granular carrier such as titania or γ-alumina is preferable. These catalysts are preferably packed in a column and reacted under heating by passing through an ammonium ion-containing wastewater to which an oxidizing agent has been added, and in this case, an upward flowing liquid is desirable. In the third step, the pH of the second step outlet treated water is 4 to 9,
Preferably, it is 6 to 8. If the pH of the treated water is less than 4, some of the nitrite ions may again be converted to nitrate ions. When the pH of the treated water exceeds 9,
The reaction rate between the ammonium ion and the oxidizing agent may be reduced. The reaction temperature is 70-300 ° C., preferably 80
To 200 ° C, more preferably 140 to 180 ° C
It is. SV is 0.5 to 20 hr ^-1 , preferably 2 to 20 hr ^-1 .
Desirably, it is 10 to 10 hr ^-1 . Hereinafter, the method of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of an example of an apparatus for performing the method of the present invention. First, the desulfurization effluent is led to the reduction tank 1 and adjusted to the optimum pH in this tank.
A metal that generates hydrogen in water is added and the nitrate nitrogen is reduced with stirring. The treated water in which the nitrate nitrogen has been reduced to nitrite nitrogen or nitrogen gas is then sent to the pretreatment tank 3 by the pump 2, the pH is adjusted, the flocculant is added, the mixture is gently stirred, and the mixture is left standing. Settle things. The supernatant is sent to a filter 5 by a pump 4 to remove fine suspended substances by filtration. The filtrate that has passed through the filter is led to a regulating tank 6, where the pH is adjusted to 6 to 8 and an oxidizing agent is added. After the pH adjustment, the treated water to which the oxidizing agent has been added is then sent by a pump 7 to a catalyst packed tower 9 via a heater 8 to cause a reaction between ammoniacal nitrogen and nitrite nitrogen. If necessary, an oxidizing agent such as hydrogen peroxide is added to the treated water that has exited the catalyst packed tower, and the treated water can be passed through the catalyst packed tower 10 to decompose ammoniacal nitrogen. After substantially completely converting the nitrogen into nitrogen gas, the treated water is discharged via the pressure regulating valve 11.

[0009]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. Example 1 380 mg / liter of ammoniacal nitrogen, 64 of nitrate nitrogen
The desulfurization effluent containing 350 mg / liter calcium and 350 mg / liter calcium was adjusted to pH 3 with sodium hydroxide,
C., and zinc powder was added at 4,000 mg / liter and stirred. Measure the concentration of nitrite nitrogen and nitrate nitrogen in the treated water after adding the zinc powder,
The state of reduction of nitrate nitrogen and formation of nitrite nitrogen were investigated. The results are shown in Table 1. The pH adjustment, heating and zinc powder addition of the desulfurization effluent were performed in the same manner as above, and zinc powder addition 3
To the treated water after 0 minute, sodium hydroxide was added to adjust the pH to 11 and zinc eluted was precipitated as zinc hydroxide. Further, sodium carbonate was added to precipitate calcium contained in the wastewater as calcium carbonate, and then an anionic flocculant (polyacrylamide hydrolyzate) was added.
After allowing the aggregates to settle by standing, the supernatant was filtered through a cartridge filter to separate fine suspended substances, and the filtrate was neutralized by adding sulfuric acid to pH 6.7. In this treated water, ammonia nitrogen remains without being decomposed,
Sodium nitrite was used at a total nitrite nitrogen concentration of 385 mg /
Liter and heated to 160 ° C.
The solution was passed through a 5 wt% platinum / titania sphere catalyst layer at SV = 3 hr ^-1 . The ammonia nitrogen in the treated water flowing out of the catalyst packed tower was 1 mg / l or less, the nitrite nitrogen 5 mg / l, the nitrate nitrogen 8 mg / l, and the nitrogen removal rate was 97%. Example 2 Using the same desulfurization waste water as in Example 1, zinc powder was
The same operation as in Example 1 was repeated except that the amount was added so as to be 0 mg / liter. Table 1 shows the concentrations of nitrite nitrogen and nitrate nitrogen in the treated water after adding the zinc powder.

[0010]

[Table 1]

The ammonia water in the treated water flowing out of the catalyst packed tower is 1 mg / l or less, the nitrite nitrogen 5 mg / l and the nitrate nitrogen 1 mg / l or less, and the nitrogen removal rate is 98% or more. Was.

[0012]

According to the method of the present invention, nitrate nitrogen in waste water containing simultaneously nitrate nitrogen and ammonia nitrogen is converted into nitrite nitrogen or nitrogen gas at a low temperature by using a metal which generates hydrogen in water in advance. The nitrate nitrogen and the ammonia nitrogen in the wastewater are gradually reduced by combining the process of removing the metal eluted by softening treatment and converting it to nitrogen by the catalytic reaction of ammonia nitrogen and nitrite. Decomposition processing can be performed efficiently under the conditions.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an example of an apparatus for performing the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reduction tank 2 Pump 3 Pretreatment tank 4 Pump 5 Filter 6 Adjustment tank 7 Pump 8 Heater 9 Catalyst filling tower 10 Catalyst filling tower 11 Pressure regulating valve

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomoyuki Asada 3-2-2, Nakanoshima, Kita-ku, Osaka Kansai Electric Power Co., Inc. (72) Inventor Hiroshi Kimoto 3-2-2, Nakanoshima, Kita-ku, Osaka Kansai Inside Electric Power Company (72) Inventor Yasuhiko Takabayashi 3-4-7 Nishi Shinjuku, Shinjuku-ku, Tokyo Kurita Industry Co., Ltd. (72) Inventor Toshiji Nakahara 3-4-2 Nishi Shinjuku, Shinjuku-ku, Tokyo Kuri (56) References JP-A-4-200790 (JP, A) JP-A-53-115557 (JP, A) JP-A-4-190882 (JP, A) JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 1 / 58,1 / 72,1 / 74

Claims (2)

(57) [Claims] 1. Wastewater containing nitrate nitrogen and ammonia nitrogen
Is contacted with a metal that generates hydrogen in water in the first step.
Touch to remove some or all of the nitrate nitrogen in the wastewater
While reducing the remaining nitrate nitrogen to nitrogen
Nitrite generated in the first step
The amount of ammonia nitrogen is less than that of ammonia nitrogen in the third step.
In the second step,
After adjusting the pH of the water to 10 or more, add a flocculant to
After removing the metal eluted by the softening treatment,
In the process, the ammonia nitrogen in the wastewater and the first process
When reacting the generated nitrite nitrogen in the presence of a catalyst,
Or the amount of nitrite nitrogen that is insufficient for the reaction equivalent
Add oxidizing agent and add ammonia nitrogen and nitrite nitrogen
A method for treating wastewater containing nitrate nitrogen and ammonia nitrogen, which comprises converting nitrogen into nitrogen . 2. The method according to claim 1 , wherein the oxidizing agent added in the third step is nitrite nitrogen.
The nitrate nitrogen according to claim 1, wherein
Wastewater containing nitrogen and ammoniacal nitrogen.